1. Testing
24-Feb-19

2. What testing is for
The point of testing is to determine whether software does what it is supposed to do
Testing also helps you discover where your error are
In this way it can greatly facilitate debugging
Scenario: Your company is being sued because some control software it wrote caused a fatal accident
Someone will be facing a long jail term
Are your JUnit tests good enough to stand up in court?
So far programmers have not been held criminally liable for dangerously poor quality code
Sooner or later, this will change

3. The Extreme Programming view
“If it isn’t tested, it’s assumed not to work”
Extreme Programming also says you should write the tests before writing the code
Reason: This helps clarify for you what the code is supposed to do
Next you run the tests
They fail, of course, because the code hasn’t been written
Then you fix the failures, one at a time
This is helpful in another way—if you come back to the code much later, the tests tell you exactly where to get started again
Of course, you can’t run the tests unless the methods exist—but they can be stubs

4. Writing tests first in Eclipse
First, write the stubs
class Token { public Token(String value, int type) { } public String getValue() { return null; } public int getType() { return 0; } public boolean equals(Object o) { return false; } }
Then in Eclipse, select the class and do File  New  Other...  Java/JUnit TestCase
Select all the methods you want to create tests for
Eclipse generates all the test stubs for you

5. Testing the boundaries
You should test not only the most common cases, but the cases “around the edges,” where things are most likely to go wrong
You’re the programmer—you should have a feel for where the special cases are likely to be

6. An example Is this a good test? Does hasNext() ever return false?
public void testHasNext() { tokenizer = new Tokenizer("hello"); assertTrue(tokenizer.hasNext()); }
Is this a good test?
Does hasNext() ever return false?
Does it return true after you get the "hello" token?
It should, if you read the assignment!
Does it return false after you get the next token, which should be the EOI (end of input) token?
It should do this, too

7. Is this a better test?
public void testHasNext() { Tokenizer tokenizer = new Tokenizer("one two three"); assertTrue(tokenizer.hasNext()); while (tokenizer.hasNext()) { Token token = tokenizer.next(); } assertFalse(tokenizer.hasNext()); }
Why not?

8. Reminder: JUnit Assert methods
assertTrue(boolean test)
assertFalse(boolean test)
assertEquals(expected, actual)
assertSame(Object expected, Object actual)
assertNotSame(Object expected, Object actual)
assertNull(Object object)
assertNotNull(Object object)
fail()
Notice the order of expected and actual
All of these can take a String as an optional first argument

9. Comments The first assignment was about using Eclipse and JUnit
Proper testing is a significant component of your grade
The emphasis on JUnit testing will continue in the following assignments
Your knowledge of JUnit and Eclipse will be tested on the first quiz

10. The End